Development of host-mimicking legume-based media for robust induction of sporulation in soybean-associated Cercospora species

Cercospora species associated with soybean cause Cercospora leaf spot and purple seed stain, which are major diseases affecting soybean production worldwide and can lead to significant yield and seed quality losses. However, inconsistent and limited sporulation under laboratory conditions remains a critical challenge, limiting morphological characterization and the establishment of reproducible experimental systems. These limitations further restrict our understanding of the biology, epidemiology, and pathogenicity of these pathogens. In this study, we developed legume-based culture media derived from soybean and pea seeds to mimic host-associated environmental conditions and compared their effects on sporulation with those of commonly used artificial media, including potato dextrose agar (PDA) and V8 juice agar. Legume-based media consistently supported higher conidial production than PDA and V8 across multiple strains, although conidial yields varied depending on the strain and medium concentration. Transcriptional analysis of sporulation-related genes revealed that abaA , wetA , and steA did not exhibit consistent medium-dependent expression patterns, whereas velB expression tended to increase on several legume-based media. Evaluation of additional field isolates recovered from soybean further showed that all tested isolates produced conidia on legume-based media, including several isolates that failed to sporulate on PDA. Overall, these findings demonstrate that soybean- and pea-based media provide practical alternatives to conventional media for inducing sporulation in soybean-associated Cercospora species under laboratory conditions.